1. Field of the Invention
This invention relates to a pneumatic radial tire, particularly for construction vehicles. The invention is concerned with improvement of durability, more particularly improvement of side cut resistance against external damage of side areas of the tire.
2. Description of the Prior Art
In general, since a pneumatic radial tire for a construction vehicle runs on rough roads, side portions can be damaged easily by stones and tree stumps. Side cuts are classified into two groups, firstly leakage of air caused by penetration in the side portion that is damaged by shock cuts, and secondly leakage of air caused by growing of cuts by repeated deformation resulting in penetration and leakage of air in the side portion. In a pneumatic radial tire for a construction vehicle, conventionally, in addition to the extension of turn-up portions of a carcass ply to around the maximum width of the tire, a side rubber 6 having good shock cut property or crack growth resistance may be arranged to extend from buttress portions of a tread to around bead portions covering the outside of a turn-up ply. This is shown in FIG. 4(a) of the accompanying drawings, which is a cross-sectional view of a tire of the prior art. Further, at least one reinforcing layer 10 may be arranged outside a main ply, which is damaged by cuts frequently, as shown in FIG. 4(b) of the accompanying drawings, which is a cross-sectional view of another tire of the prior art.
It is an object of the present invention to restrain speed of cut growth resulting from leakage of air caused by repeated deformation in a pneumatic radial tire for a construction vehicle without deteriorating other aspects of the tire performance.